Property Based Testing

This generates random inputs to verify your code satisfies general properties rather than just testing handpicked examples. It's great for catching edge cases you'd never think to test manually, like testing that reversing a string twice returns the original or that sorting preserves length. The skill covers Hypothesis for Python, fast-check for JavaScript, and junit-quickcheck for Java. The real value is in the shrinking: when a test fails, these tools automatically minimize the failing input to show you the simplest case that breaks your code. Works best alongside traditional tests, not as a replacement, and you need to think carefully about what properties actually matter rather than just restating your implementation.